In a stringed instrument such as a guitar, a string retainer sets the break angle of the strings over the nut or zero fret. This alleviates the need to angle the headstock backward in order to achieve a desired break angle. It may take the form of a bar under which all strings pass, or individual “string trees” as found on Fender™ designs.
Many guitar designs have included a vibrato system, which allows the user to shift the pitch of the strings through a movable bridge attached to an actuator bar. Examples of this include the Kauffman Vibrola (1929), the Bigsby Virato (1952), and the Fender Stratocaster “Floating Tremolo” (1954). Vibrato bridges are quite popular today.
A problem with these systems is the tendency of the use of the vibrato bar to throw the instrument out of tune. This occurs because the change in string length that creates the pitch shift also causes the string to travel across the nut or zero fret, and friction effects prevent it from returning to its original position upon release of the vibrato bar.
There are two approaches to solving this problem: (1) reducing the string friction at the nut to near zero, and (2) reducing the motion of the string across the nut to near zero. The search for solutions led to the development of the “double locking tremolo” (zero travel) such as the Floyd Rose system, and “roller nut” (zero friction) such as the Fender/LSR system. The main problem with locking nut systems is that the clamping action of the nut moves the string vertically and thus knocks the instrument out of tune, so that a special bridge with fine-tuning adjusters on the bridge is required. A side-locking nut design was introduced by Super Vee in 2007. This system has the advantage of eliminating vertical motion of the string upon locking the nut. This system has not been widely adopted, and the roller nut has had limited popularity. The double locking tremolo, however, has achieved very widespread use. This is in spite of the fact that there are serious convenience of use problems with them. If the actuation of the locking mechanism disturbs the pitch of the strings, a locking nut cannot be employed on a guitar with a standard bridge. Also, retuning is cumbersome: the nut must be unlocked (often requiring the use of tools), and the fine tuners centered. The instrument is tuned using the tuning keys as normal, the nut is relocked, and the instrument is retuned using the fine tuners.
What is needed is a device that achieves easy clamping and unclamping of the strings near the nut with near zero displacement, vertical or horizontal, that can be fitted to a guitar with a standard tremolo bridge.